Deactivation of a Zn/TiO<Subscript>2</Subscript> catalyst in the course of methanol steam reforming in a microchannel reactor

The service life tests of a Zn/TiO₂ catalyst deposited on the microchannel plates of copper foam, nickel foam, and corrugated brass foil in the process of methanol steam reforming demonstrated that the catalyst stability and operation time depend on microchannel plate material. The rate of catalyst deactivation correlated with the thermal conductivity of the microchannel plate material. It was found that catalyst deactivation resulted from the decomposition of zinc titanates, which are active components, and it was accompanied by the appearance of a zinc oxide phase. The best results in the service life tests were obtained with the microchannel plates of copper foam. A microchannel reactor containing 16 copper plates continuously operated at 400°C for 150 h; in this case, the conversion of methanol decreased by 8%. The subsequent microreactor operation for 500 h caused a decrease in the methanol conversion by 26%. It was found that the loss of the catalyst activity was a reversible process, and the activity can be restored by annealing in air.     

甲醇水蒸气重整制氢Cu/ZnO/Al2O3催化剂的研究

燃料电池作为一种无污染、高效率的能源引起世界各大汽车公司的广泛关注[1,2]。用于燃料电池的燃料目前研究较多的是氢气,用氢气作燃料存在储存、安全、运输等问题,寻求合适贮氢方法或替代燃料,实现车载制氢是解决问题的办法。甲醇作为液体燃料,因具有高能量密度,低碳含量,以及运输和贮存等优势成为车载制氢的理想燃料,甲醇水蒸气重整制氢反应也成为研究的热点[3～10]。车载制氢对甲醇水蒸气重整制氢反应体系中的产氢速率,氢气和CO的含量都有一定的要求。尤其对CO含量要求更为苛刻,因CO易引起燃料电池阳极催化剂中毒[11,12]。因此,开…     

Effect of the microchannel plate design on the capacity of methanol steam reformers

Methanol steam reforming in microreactors is considered, and the effects of the microreactor geometry (cylindrical and rectangular) and microchannel plate (MCP) design on the hydrogen capacity of the microreactor is analyzed. The MCPs were made from aluminum foil, stainless steel, and foamed nickel by laser engraving, electrochemical etching, and pressing. The amount of catalyst powder (CuO/ZnO = 40: 60 mol/mol) fixed on one MCP was 0.04–2.5 g. The specific hydrogen capacity (U _w) of the cylindrical microreactor is more than 3 times as high as the U _w of the rectangular microreactor and is 6 times as high as the U _w of a conventional fixed-bed catalytic reactor. This gain in hydrogen capacity is due to the more efficient use of the catalyst in the microreactors. The MCP design, which determines the residence time of the reactants in the microreactor, also has a significant effect on the capacity of the microreactor.     

Hydrogen production by steam reforming of glycerol over Ni/Ce/Cu hydroxyapatite-supported catalysts

Hydroxyapatite-supported Ni-Ce-Cu catalysts were synthesised and tested to study their potential for use in the steam reforming of glycerol to produce hydrogen. The catalysts were prepared by the deposition-precipitation method with variable nickel, cerium, and copper loadings. The performance of the catalysts was evaluated in terms of hydrogen yield at 600°C in a tubular fixed-bed microreactor. All catalysts were characterised by the BET surface area, XRD, TPR, TEM, and FE-SEM techniques. The reaction time was 240 min in a fixed-bed reactor at 600°C and atmospheric pressure with a water-to-glycerol feed molar ratio of 8: 1. It was found that the Ni-Ce-Cu (3 mass %-7.5 mass %-7.5 mass %) hydroxyapatite-supported catalyst afforded the highest hydrogen yield (57.5 %), with a glycerol conversion rate of 97.3 %. The results indicate that Ni/Ce/Cu/hydroxyapatite has great potential as a catalyst for hydrogen production by steam reforming of glycerol.     

甲醇POSR制氢的反应网络热力学分析和有效因子的估算

在Cu/ZnO/Al2O3催化剂上对甲醇部分氧化蒸汽重整制备氢气反应的动力学过程进行了研究。在常压和473 K～1 073 K温度范围内对该反应网络中的甲醇部分氧化、甲醇蒸汽重整、甲醇分解和水煤气反应的化学平衡进行了分析。在对这些反应的催化剂Cu/ZnO/Al2O3动力学研究的基础上，根据有效因子的基本概念，考虑催化剂颗粒内的扩散限制，对每个反应沿反应器床层的有效因子进行了估算。     

Initiation behaviour in hydrogenation of pyrolysis gasoline over presulphided Ni-Mo-Zn/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

A presulphided treatment was applied to the oxidic Ni-Mo-Zn/Al₂O₃ catalyst (nickel catalyst) in order to avoid thermal run-away during initiation of the hydrogenation of pyrolysis gasoline. The physico-chemical properties of the prepared oxidic nickel catalyst, the reduced and passivated (RP) nickel catalyst and the sulphided (RPS) nickel catalyst were characterised using N₂ adsorption-desorption, X-ray diffraction, temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The TPR results showed that the reducibility of the RP Ni-Mo-Zn/Al₂O₃ catalyst was improved over the oxidic nickel catalyst. The XPS spectra confirmed the binding energy of the RPS nickel catalyst to be higher than that of the oxidic nickel catalyst. The catalytic performance was evaluated on a fixed-bed reactor (reaction temperature between 30 °C and 70°C, at 2.8 MPa of total pressure and weight hourly space velocity of 2.0 h^?1, the volume of H₂/pyrogasoline = 200: 1). The rising temperature of the RPS nickel catalyst was almost 20°C lower than that of the oxidic nickel catalyst during the initial stage of the hydrogenation reaction. The results indicated that the RPS nickel catalyst exhibited better stability than the oxidic nickel catalyst during the start-up period, thereby providing a better selectivity in long-term operation.     

Kinetics of methanol steam reforming over COPZr-2 catalyst

The COPZr-2 catalyst, which was prepared in our prophase research, showed good catalytic performance in methanol steam reforming reaction. In this article, the best one was chosen as an example to study the reaction kinetics of methanol steam reforming over this type of catalyst. First, the effects of methanol conversion to outlet CO2 and methanol conversion to outlet CO on methanol pseudo contact time W/FMeOH were investigated. Then by applying the reaction route that methanol direct reforming （DR） and methanol decomposition （DE） were carried out in parallel, the reaction kinetic model with power function type was established. And the parameters for the model were estimated using a non-linear regression program which computed weighted least squares of the defined objects function. Finally, the kinetic model passed the correlation test and the F-test.     

Steam Reforming Reactions of Methanol Over Nickel and Copper Catalysts

Steam-reforming reactions of methanol over NiO/Al₂O₃ and CuO/ZnO have been investigated. Over the nickel catalyst, the reaction rate is of zero kinetic order with respect to either methanol or steam, and the activation energy is 12.4 kJmol^?1, whereas with copper catalyst, the rate is expressed according to the literature as kP_a/(1 + K_aP_a + K_b+P_b) in which “a” and “b” are methanol and steam, respectively. The rate-controlling step of the reaction is assigned to the dissociation of O-H bond with dehydrogenation of C-H bond proceed rapidly to form carbon oxides. With copper catalyst the intrinsic participation of a water molecule during the dehydrogenation of C-H bond leads to the formation of carbon dioxide. With nickel catalyst, the dehydrogenation proceed more rapidly than the migration of a water molecule from an alumina site to a nickel site and causes almost exclusively the formation of carbon monoxide and hydrogen at a lower reaction temperature.     

橄榄石对甲苯催化重整反应的影响

在固定床反应器上,以甲苯为生物质气化焦油的模型化合物,对橄榄石以及其负载镍催化剂对甲苯裂解反应和甲苯/水蒸气重整反应的催化性能进行了研究,并对催化剂进行了SEM、BET、XRD、H₂-TPR等表征。结果表明,煅烧使原矿的物化特性发生改变,橄榄石对甲苯裂解反应和重整反应有一定的催化活性。而Ni的引入,使催化剂对甲苯裂解反应的活性有所降低,甲苯的转化率降低2.2%~9.8%;但催化剂对甲苯/水蒸气重整反应的活性升高,甲苯的转化率可高达97.0%,并且载镍橄榄石催化剂对甲苯/水蒸气重整反应有较强的稳定性。     

Selective CO oxidation on a Ru/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst in the surface ignition regime: 1. Fine purification of hydrogen-containing gases

Selective CO oxidation in a mixture simulating the methanol steam reforming product with an air admixture was studied over Ru/Al₂O₃ catalysts in a quasi-adiabatic reactor. On-line monitoring of the gas temperature in the catalyst bed and of the residual CO concentration at different reaction conditions made it possible to observe the ignition and quenching of the catalyst surface, including transitional regimes. A sharp decrease in the residual CO concentration takes place when the reaction passes to the ignition regime. The evolution of the temperature distribution in the catalyst bed in the ignition regime and the specific features of the steady-state and transitional regimes are considered, including the effect of the sample history. In selective CO oxidation and in H₂ oxidation in the absence of CO, the catalyst is deactivated slowly because of ruthenium oxidation. In both reactions, the deactivated catalyst can be reactivated by short-term treatment with hydrogen. A 0.1% Ru/Al₂O₃ catalyst is suggested. In the surface ignition regime, this catalyst can reduce the residual CO concentration from 0.8 vol % to 10–15 ppm at O₂/CO = 1 even in the presence of H₂O and CO₂ (up to ～20 vol %) at a volumetric flow rate of ～100 1 (g Cat)^?1 h^?1, which is one magnitude higher than the flow rates reported for this process in the literature.     

CeO2改性Cu/Al2O3催化剂上甲醇水蒸气重整制氢

研究CeO2改性Cu/Al2O3催化剂上甲醇水蒸气重整制氢反应过程,得到低温活性、氢选择性和稳定性较好的催化剂.Cu/Al2O3催化剂中添加CeO2提高了催化剂的活性和稳定性,当CeO2质量分数为20％时,催化剂活性表现最佳.在反应温度250 ℃,水醇摩尔比为1.0,液体空速为3.28 h －1条件下,甲醇转化率为95.5％,氢气选择性为100％.此外,CeO2通过促进水气转化反应降低了重整气中CO的含量.Cu/CeO2/Al2O3催化剂在200 h的寿命实验中,活性仍保持在90.0％以上,而Cu/Al2O3催化剂在100 h的寿命实验中,活性已很快下降.XRD和TPR分析及表面元素分布结果表明,铜和铈相互作用促进了铜在催化剂表面的高度分散,阻止了铜晶粒团聚、烧结,促使铜晶粒细小化,促进了铜的还原,改善了Cu/CeO2/Al2O3催化剂的性能.     

CeO_2改性Cu/Zn-Al水滑石衍生催化剂对甲醇水蒸气重整制氢性能的影响

采用原位合成法在γ-Al2O3表面合成了锌铝水滑石,再采用顺次浸渍法制备了Ce/Cu/Zn-Al催化材料;将其应用于甲醇水蒸气重整制氢,探讨了Ce含量对Cu/Zn-Al催化剂催化性能的影响.催化剂表征结果表明,CeO_2的引入改善了活性组分铜的分散度、铜的比表面积以及催化剂的氧化还原性质,进而提高了催化剂的催化活性和产氢率.当Ce含量为4%时,催化剂活性最佳,在250℃时,甲醇转化率达到100%,CO摩尔分数为0.39%,与Cu/Zn-Al催化剂相比,甲醇转化率提高了近40%.     

Structured Catalysts Prepared by Electroless Plating Technique onto a Metal Substrate, for a Wall-Type Hydrogen Production System

This article reviews our works on the structured catalysts for a wall-type hydrogen production system including methanol steam reforming (MSR), CO shift reaction (CO SR) and methanol decomposition (MD). The structured catalysts were copper-based, palladium-based and nickel-based catalysts. Such a series of structured catalysts were prepared by the electroless plating technique that is a novel method for preparing a structured type catalyst onto a metal-substrate. The copper-based catalyst exhibited high performance for MSR and CO SR, the palladium-based catalyst high for MSR, and the nickel-based catalyst high for MD. The catalytic properties of these catalysts were affected by the difference of the plating condition and the pretreatment condition prior to the reaction. In the copper-based catalyst, the reforming and shift activities were enhanced by the oxidation treatment. One of the factors of such activity enhancement by the oxidation was thought to be in close proximity existence of copper and zinc atoms. A lot of monodentate-type formate species having high reactivity was formed on the oxidized catalyst, which would be correlated to the activity enhancement. In the palladium-based catalyst, the reforming activity was improved by the continuous reduction treatment followed by the oxidation. Such continuous pretreatment formed the PdZn alloy species thought to be a reforming site in the surface layer. The decomposition performance of the nickel-based catalyst depended on the ratio of the crystallite size of nickel particles to that of aluminum particles. The electronic influence of zinc and phosphorous components incorporated in the plated layer contributed to the improvement of the selectivity of product.     

Bimetallic Rh-Co/ZrO<Subscript>2</Subscript> catalysts for ethanol steam reforming into hydrogen-containing gas

The properties of supported bimetallic Rh-Co/ZrO₂ catalysts in ethanol steam reforming into hydrogen-containing gas were studied. The particles of Rh-Co solid solutions on the catalyst surface were prepared by the thermal decomposition of the double complex salt [Co(NH₃)₆][Rh(NO₂)₆] and the solid solution Na₃[RhCo(NO₂)₆]. It was found that the bimetallic Rh-Co/ZrO₂ catalysts exhibited high activity in the reaction of ethanol steam reforming. The equilibrium composition of reaction products was attained at 500–700°C and a reaction mixture space velocity of 10000 h⁻¹.     

二甲醚水蒸气重整制氢的ZSM-5和Cu-Zn的复合催化体系

二甲醚水蒸气重整制氢反应是燃料电池理想的供氢方式之一.探讨了二甲醚水蒸气重整过程中的反应与反应、反应与传热的耦合协同效应.采用二甲醚水解催化剂ZSM-5(硅铝比为25)和甲醇水蒸气重整催化剂(Cu-Zn系列及商用Cu-Zn-Al催化剂)混合制得二甲醚水蒸气重整的复合催化剂.在固定床反应装置中评价了催化剂活性并对催化剂进行了透射电镜、X射线衍射及N2吸附表征.结果表明,复合催化剂的活性除了受催化剂组成和铜含量的影响外,还与Al和Zr的量有关.在Cu:Zn摩尔比为60:30时,Al和Zr的同时加入使催化剂中Cu晶粒分散最好,催化剂具有较高的低温活性,二甲醚在空速为4 922 ml/(g·h)和260℃下的转化率达到72%.     

微通道反应器内"就地"合成沸石膜催化层及其性能

采用简单、新颖的沸石粒子引入方法,将NaX沸石晶种引入不锈钢微反应器的微通道内,并用流动法"就地"直接在微通道内通过沸石生长形成NaX沸石膜层,经铯离子交换处理成为CsNaX催化层,用苯甲醛和氰基乙酸乙酯的Knoevenagel缩合反应评价了该催化层的催化性能.结果表明,微通道内形成的沸石膜层连续,均匀,具有良好的催化功能.微反应器内缩合反应的结果明显优于传统反应器.     

湿混法制备甲醇氧化重整制氢CuZnAlZr催化剂

用简易湿混法制备了用于甲醇氧化重整制氢的CuZnAlZr催化剂,与共沉淀法制备的催化剂比较,结果表明,湿混法制备的催化剂具有相当的中高温活性和略低的低温活性,有较高的CO2选择性。XRD、TPR、TG-DSC等表征结果显示,湿混法制备的催化剂中铜组分易于向表面迁移和富集,并可能与氧化铝作用生成铜铝复合氧化物,具有了更高的Cu分散度和Cu0比表面浓度。湿混法制备的催化剂对甲醇氧化重整反应有较好的稳定性,经100 h的连续反应,在275 ℃时甲醇转化率在90％以上,重整气中氢气体积分数大于60％,CO2选择性接近99％。     

CH_4-H_2O-CO_2转化制取合成甲醇原料气的研究Ⅲ.镍催化剂活性降低原因的探讨

在变温床中考查了负载型镍催化剂用于ＣＨ４Ｈ２ＯＣＯ２转化制取合成气的活性与稳定性，该过程所制得的合成气勿需分离即可直接用于合成甲醇。本文对催化剂活性下降的原因用比表面、孔结构、ＸＲＤ和ＸＰＳ对不同反应时间的催化剂进行了对比分析，发现镍催化剂活性降低的原因是催化剂表面镍的大量流失。     

甲烷三重整制合成气

甲烷三重整是利用CO₂-H₂O-O₂ 同时重整甲烷的过程。该工艺既可以生产H₂/CO 为1.5 —2.0的合成气,又可以缓解甚至消除催化剂的积炭,适合于更廉价地生产用于合成甲醇、二甲醚以及清洁燃料等下游产品的合成气。本文重点评述了近年来国内外甲烷三重整制合成气在热力学、催化剂、反应器、动力学等方面的研究进展,指出甲烷三重整反应在电厂烟气、煤层气、天然气综合利用方面具备良好前景,但要通过该过程实现廉价合成气的生产,仍需研制高活性、抗积炭性能强的催化剂,并对反应器进行改进,以及进行反应机理和反应动力学的深入研究。     

Synthesis and Characterization of AlPO<Subscript>4</Subscript>/ZSM-5 Catalyst for Methanol Conversion to Dimethyl Ether

A catalyst based on zeolite was synthesized using the hydrothermal method, and alumina phosphate was embedded in its structure. The correspondent reactor tests were carried out to assess the synthesized catalyst where methanol with a purity of 99.9% was used. The results indicated that alumina phosphate is considerably effective on catalyst functionality. Given the results, the best performance was obtained when the ratio of alumina phosphate to alumina is 0.7 weighted in catalyst and fixed-bed reactor serves in a temperature of 300°C and WHSV of 0.8 h^?1. Structure and morphology of synthesized catalyst were characterized by BET, XRF, SEM, and XRD. The catalyst was evaluated in the process of converting methanol to dimethyl ether in a fixed-bed reactor under operating conditions of 300°C, 1 atm and 0.5 mL min^?1 of feed (pure methanol). The results of test indicated by increasing the amount of alumina phosphate to alumina, the conversion rate of methanol was increased to a constant value and does not change in ratios higher than 0.7. Moreover, the methanol conversion rate will reach temperature 300°C at 84%.